More and more people pay attention to the safety of electrical measurement. At present, about 9,000 workers are disabled during electrical measurement every day, and more than 80% of the accidents are caused by operation error in use of the measuring instruments. In the art, the related measuring meter needs to switch among dozens of gears to select a function matching the type of the signal to be measured, otherwise leads the accidents, such as using AC voltage measuring function to measure DC voltage, using resistance measuring function to measure AC voltage, and etc.